// 判断是否是ie
var isIE = (document.all) ? true : false
//封装 $方法
var $ = function (id) {
  return 'string' == typeof id ? document.getElementById(id) : id
}

//定义class对象
var Class = {
  create: function () {
    return function () { this.initialize.apply(this, arguments) }
  }
}

var Extend = function (destination, source) {
  for (var property in source) {
    destination[property] = source[property]
  }
}

var Bind = function (object, fun) {
  return function () {
    return fun.apply(object, arguments)
  }
}

var BindAsEventListener = function (object, fun) {
  return function (event) {
    return fun.call(object, (event || window.event))
  }
}

var CurrentStyle = function (element) {
  return element.currentStyle || document.defaultView.getComputedStyle(element, null)
}

function addEventHandler (oTarget, sEventType, fnHandler) {
  if (oTarget.addEventListener) {
    oTarget.addEventListener(sEventType, fnHandler, false)
  } else if (oTarget.attachEvent) {
    oTarget.attachEvent('on' + sEventType, fnHandler)
  } else {
    oTarget['on' + sEventType] = fnHandler
  }
}

function removeEventHandler (oTarget, sEventType, fnHandler) {
  if (oTarget.removeEventListener) {
    oTarget.removeEventListener(sEventType, fnHandler, false)
  } else if (oTarget.detachEvent) {
    oTarget.detachEvent('on' + sEventType, fnHandler)
  } else {
    oTarget['on' + sEventType] = null
  }
}

//拖放程序
var Drag = Class.create()
Drag.prototype = {
  //拖放对象
  initialize: function (drag, options) {
    this.Drag = $(drag)//拖放对象
    this._x = this._y = 0//记录鼠标相对拖放对象的位置
    this._marginLeft = this._marginTop = 0//记录margin
    //事件对象(用于绑定移除事件)
    this._fM = BindAsEventListener(this, this.Move)
    this._fS = Bind(this, this.Stop)

    this.SetOptions(options)

    this.Limit = !!this.options.Limit
    this.mxLeft = parseInt(this.options.mxLeft)
    this.mxRight = parseInt(this.options.mxRight)
    this.mxTop = parseInt(this.options.mxTop)
    this.mxBottom = parseInt(this.options.mxBottom)

    this.LockX = !!this.options.LockX
    this.LockY = !!this.options.LockY
    this.Lock = !!this.options.Lock

    this.onStart = this.options.onStart
    this.onMove = this.options.onMove
    this.onStop = this.options.onStop

    this._Handle = $(this.options.Handle) || this.Drag
    this._mxContainer = $(this.options.mxContainer) || null

    this.Drag.style.position = 'absolute'
    //透明
    if (isIE && !!this.options.Transparent) {
      //填充拖放对象
      with (this._Handle.appendChild(document.createElement('div')).style) {
        width = height = '100%'
        backgroundColor = '#fff'
        filter = 'alpha(opacity:0)'
        fontSize = 0
      }
    }
    //修正范围
    this.Repair()
    addEventHandler(this._Handle, 'mousedown', BindAsEventListener(this, this.Start))
  },
  //设置默认属性
  SetOptions: function (options) {
    this.options = {//默认值
      Handle: '',//设置触发对象（不设置则使用拖放对象）
      Limit: false,//是否设置范围限制(为true时下面参数有用,可以是负数)
      mxLeft: 0,//左边限制
      mxRight: 9999,//右边限制
      mxTop: 0,//上边限制
      mxBottom: 9999,//下边限制
      mxContainer: '',//指定限制在容器内
      LockX: false,//是否锁定水平方向拖放
      LockY: false,//是否锁定垂直方向拖放
      Lock: false,//是否锁定
      Transparent: false,//是否透明
      onStart: function () {},//开始移动时执行
      onMove: function () {},//移动时执行
      onStop: function () {}//结束移动时执行
    }
    Extend(this.options, options || {})
  },
  //准备拖动
  Start: function (oEvent) {
    if (this.Lock) { return }
    this.Repair()
    //记录鼠标相对拖放对象的位置
    this._x = oEvent.clientX - this.Drag.offsetLeft
    this._y = oEvent.clientY - this.Drag.offsetTop
    //记录margin
    this._marginLeft = parseInt(CurrentStyle(this.Drag).marginLeft) || 0
    this._marginTop = parseInt(CurrentStyle(this.Drag).marginTop) || 0
    //mousemove时移动 mouseup时停止
    addEventHandler(document, 'mousemove', this._fM)
    addEventHandler(document, 'mouseup', this._fS)
    if (isIE) {
      //焦点丢失
      addEventHandler(this._Handle, 'losecapture', this._fS)
      //设置鼠标捕获
      this._Handle.setCapture()
    } else {
      //焦点丢失
      addEventHandler(window, 'blur', this._fS)
      //阻止默认动作
      oEvent.preventDefault()
    }

    //附加程序
    this.onStart()
  },
  //修正范围
  Repair: function () {
    if (this.Limit) {
      //修正错误范围参数
      this.mxRight = Math.max(this.mxRight, this.mxLeft + this.Drag.offsetWidth)
      this.mxBottom = Math.max(this.mxBottom, this.mxTop + this.Drag.offsetHeight)
      //如果有容器必须设置position为relative或absolute来相对或绝对定位，并在获取offset之前设置
      !this._mxContainer || CurrentStyle(this._mxContainer).position == 'relative' || CurrentStyle(this._mxContainer).position == 'absolute' || (this._mxContainer.style.position = 'relative')
    }
  },
  //拖动
  Move: function (oEvent) {
    //判断是否锁定
    if (this.Lock) {
      this.Stop()
      return
    }

    //清除选择
    window.getSelection ? window.getSelection().removeAllRanges() : document.selection.empty()
    //设置移动参数
    var iLeft = oEvent.clientX - this._x, iTop = oEvent.clientY - this._y
    //设置范围限制
    if (this.Limit) {
      //设置范围参数
      var mxLeft = this.mxLeft, mxRight = this.mxRight, mxTop = this.mxTop, mxBottom = this.mxBottom
      //如果设置了容器，再修正范围参数
      if (!!this._mxContainer) {
        mxLeft = Math.max(mxLeft, 0)
        mxTop = Math.max(mxTop, 0)
        mxRight = Math.min(mxRight, this._mxContainer.clientWidth)
        mxBottom = Math.min(mxBottom, this._mxContainer.clientHeight)
      }

      //修正移动参数
      iLeft = Math.max(Math.min(iLeft, mxRight - this.Drag.offsetWidth), mxLeft)
      iTop = Math.max(Math.min(iTop, mxBottom - this.Drag.offsetHeight), mxTop)
    }
    //设置位置，并修正margin
    if (!this.LockX) { this.Drag.style.left = iLeft - this._marginLeft + 'px' }
    if (!this.LockY) { this.Drag.style.top = iTop - this._marginTop + 'px' }
    //附加程序
    this.onMove()
  },
  //停止拖动
  Stop: function () {
    //移除事件
    removeEventHandler(document, 'mousemove', this._fM)
    removeEventHandler(document, 'mouseup', this._fS)
    if (isIE) {
      removeEventHandler(this._Handle, 'losecapture', this._fS)
      this._Handle.releaseCapture()
    } else {
      removeEventHandler(window, 'blur', this._fS)
    }

    //附加程序
    this.onStop()
  }
}